Lewis Hamilton's Mercedes car suffered an early stoppage on the opening morning of the two-day test at Bahrain.

Underling the importance Mercedes, beaten to victory at the desert circuit in Sunday's grand prix, are attaching to the event, both Hamilton, who rarely runs during in-season testing, and team-mate Valtteri Bottas will participate this week.

But Hamilton's running hit an early glitch when his car required a lift back to the pits within the opening hour.

The cause of the breakdown isn't known but only resulted in a 30-minute delay for Hamilton before he returned to the track.

After two hours of running, Hamilton topped the timesheets - but with a lap almost four seconds slower than Bottas' pole position on Saturday.

Mercedes will be focused on improving their long-run form during the test, with the W08 seemingly harder on its rubber than title rivals Ferrari during the opening three races of 2017.

Championship leader Sebastian Vettel is also in action at the test but the Ferrari driver will be testing Pirelli's 2018 tyres on Tuesday before reverting to normal testing on Wednesday.

Oliver Turvey will be behind the wheel of the McLaren-Honda after the team rejected the opportunity to familiarise Jenson Button with their 2017 car ahead of his return at next month's Monaco GP.

Although Honda have indicated they will be testing 'new ideas' this week, a full upgrade of their troublesome engine is not expected for another month.

Indonesian F2 driver Sean Gelael is debuting for Toro Rosso.

But the 20-year-old also suffered an early setback when his car crawled to a halt, triggering the second red-flag stoppage of the opening hour.

Renault have also confirmed they will be using the test to introduce the 'first major upgrades of a season that will see a lot of progress and improvement.'

Lewis Hamilton's Mercedes car suffered an early stoppage on the opening morning of the two-day test at Bahrain.

Underling the importance Mercedes, beaten to victory at the desert circuit in Sunday's grand prix, are attaching to the event, both Hamilton, who rarely runs during in-season testing, and team-mate Valtteri Bottas will participate this week.

But Hamilton's running hit an early glitch when his car required a lift back to the pits within the opening hour.

The cause of the breakdown isn't known but only resulted in a 30-minute delay for Hamilton before he returned to the track.

After two hours of running, Hamilton topped the timesheets - but with a lap almost four seconds slower than Bottas' pole position on Saturday.

Mercedes will be focused on improving their long-run form during the test, with the W08 seemingly harder on its rubber than title rivals Ferrari during the opening three races of 2017.

Championship leader Sebastian Vettel is also in action at the test but the Ferrari driver will be testing Pirelli's 2018 tyres on Tuesday before reverting to normal testing on Wednesday.

Oliver Turvey will be behind the wheel of the McLaren-Honda after the team rejected the opportunity to familiarise Jenson Button with their 2017 car ahead of his return at next month's Monaco GP.

Although Honda have indicated they will be testing 'new ideas' this week, a full upgrade of their troublesome engine is not expected for another month.

Indonesian F2 driver Sean Gelael is debuting for Toro Rosso.

But the 20-year-old also suffered an early setback when his car crawled to a halt, triggering the second red-flag stoppage of the opening hour.

Renault have also confirmed they will be using the test to introduce the 'first major upgrades of a season that will see a lot of progress and improvement.'

PROBLEMS WITH VETTEL'S FERRARI
Sebastian Vettel is suffering from technical problems. Pirelli has asked teams to be allowed to make up the lost time after 6pm tonight, running under lights at Bahrain International Circuit.

Dedication, he has the same mentality as Schumacher, MSC wanted to know everything down to the fine details. Drivers like Hamilton is not bothered on that side of things he just wants to get into a car and drive it. Example is last year Baku GP when Hamilton couldn't figure out how to sort the issue out with his car but Rosberg managed to do it quite easily.

Dedication, he has the same mentality as Schumacher, MSC wanted to know everything down to the fine details. Drivers like Hamilton is not bothered on that side of things he just wants to get into a car and drive it. Example is last year Baku GP when Hamilton couldn't figure out how to sort the issue out with his car but Rosberg managed to do it quite easily.